Various types of devices are known for the delivery of active ingredients in a controlled manner to the gastrointestinal tract for absorption into the systemic circulation so as to maximise the efficacy of such active ingredients.
Our International Publication WO 94/01165 describes and claims a medication administering device which comprises a housing of a size enabling it to be introduced into a body cavity. The housing, which is of a material insoluble in body cavity fluids, but which is provided with an opening, is divided into first and second expansible and contractible chambers by a displaceable member. The second chamber includes electrically-controlled means for generating a gas to expand said chamber and force medication contained in the first chamber out through the opening into the body cavity and thus is based on electrolytic technology. The device of our International Publication WO 94/01165 is an example of what is referred to as a "smart" pill.
A "smart" pill is described briefly in Popular Science, May 1992, at page 25. The "smart" pill in question is in the form of a capsule containing a tiny radio transmitter that transmits a continuous signal as it passes through the body so as to enable its location in the body to be detected at any given time. When it reaches a predetermined location, a computer signals the pill to release the medication contained therein by actuating a piston within the capsule to force out medication contained within a chamber in the capsule.
The device of our International Publication WO 94/01165 includes, in certain embodiments, an electrolytic cell and a small battery with associated electronics. In other embodiments, however, the power source is derived from two fine wires of diverse metals wrapped around the exterior surface of the housing. The two wires, in combination with the gastric fluids in which they are immersed and by which they are separated, act as a voltaic cell which is used as the power source for an electrolytic cell within the second chamber.
Thus, although the requirement for a battery is obviated, there are certain drawbacks associated with this method of generating a gas within the second chamber.
Firstly, it is not always possible to achieve the desired rates of gas generation, since the rate of gas generation is directly dependent upon the current passing through the electrolytic cell. This current depends in turn, upon the resistance provided by the electrolytic cell and the magnitude of voltage generated by the voltaic cell on the external surface of the housing. The voltage generated is not always sufficient to drive the electrolytic cell at the desired rate.
Secondly, it is undesirable to use the gastric fluids as the electrolyte for a battery, since the chemical reactions occurring at the electrodes may lead to undesirable products (such as metallic compounds or gases) being created within and released into the gastrointestinal tract.
Thus, it is an object of the present invention to overcome the problems indicated above and to provide a device which is structurally more simple, which is cheaper and easier to manufacture, and which is more compact and more efficient than the devices of the prior art.